Method of manufacturing a field joint coating

ABSTRACT

A method of manufacturing a Field Joint Coating (FJC) for a pipeline, the method comprising: providing a pipe section to be joined to a similar pipe section or free end of a pipeline, wherein each pipe section is provided with a coating comprising a thermal insulation layer over a length of the pipe section having a protruding section, wherein the end zones of each pipe section are free of thermal insulation, thereby allowing access to the ends of the pipe section and the pipeline to connect the pipe section with the free end of the pipeline, applying an anti-corrosion coating layer on a connection region of the joined ends of the pipe section and the pipeline, heating the protruding section and applying an intermediate coating layer of a thermoplastic material on the anti-corrosion coating layer and the protruding section, applying a thermal insulation layer on the intermediate coating layer.

This application is the National Stage of International Application No.PCT/NL2013/050267, filed Apr. 12, 2013, which claims benefit ofNetherlands Patent Application No. 2008638, filed Apr. 13, 2012, andwhich claims benefit of U.S. Provisional Application No. 61/623,709,filed Apr. 13, 2012.

FIELD OF THE INVENTION

The present invention relates to a method and device for manufacturing afield joint coating. The present invention further relates to a pipelinecomprising a joint.

DESCRIPTION OF THE PRIOR ART

Pipelines are used in the oil and gas industry for the transportation ofhydrocarbons. When hydrocarbon deposits are found under the sea floor,pipelines are often laid on the sea floor for transporting thehydrocarbons to a storage or production facility.

Pipelines are typically formed from many pipe sections that are weldedend-to-end before they are laid. The pipe sections are oftenmanufactured from carbon steel and are prone to corrosion if they arenot protected from the sea water. The pipe sections are therefore coatedwith protective material, the type of which may be determined by theoperating environment. Polyolefins, such as polypropylene (PP), arewidely used as a coating material. Also, other materials are used.

The outer pipe surface of the pipe section may first be provided with alayer of an anti-corrosion agent such as an epoxy, that is appliedeither in liquid or powdered form. Fusion Bonded Epoxy (FBE) is widelyused. Subsequently, the pipe coating made from, for example, apolyolefin material is provided on the anti-corrosion layer. An adhesionpromoter may be applied on top of the FBE to enhance bonding to thematerial of the pipe coating. Further coatings including insulationlayers may be applied over these coatings.

Generally, the coating layers are applied in a well-controlled orfactory environment, whereby the pipe ends of the pipe sections are notcovered by the pipe coating. The factory applied pipe coating extendsalong a length of the pipe member and ends at a first coating end facelocated at a distance from the first pipe end and at a second coatingend face located at a distance from the second pipe end.

To produce a pipeline, the pipe ends of the pipe sections are joinedtogether, generally by welding. Other joining techniques may be used.The pipe sections are joined at a pipe joint, such that the coating endfaces of the pipe sections are located at opposite sides of the pipejoint.

After the joining of the pipe sections, the pipe ends and the pipe jointneed to be covered by a joint coating. The joint coating should bondwith the factory applied pipe coating, in order to protect the pipeduring its working lifetime on the seafloor, which may be about 40years. The pipe sections are joined together in the field before theyare installed in the sea, either as risers between the seafloor and thesurface, or laid on the seabed. Pipes can be installed by J-lay or S-layor reeled onto a reel before transport to a pipelay vessel. The coatingof the pipe joints is therefore performed in the field. This means thatsaid operations may take place outside of a factory environment, such asat an onshore spool base, a quay or off-shore on the pipelay vessel,where it can be difficult to achieve optimal conditions for coating Thecoating of the joint is generally referred to as a Field Joint Coatingin the field of the art, and abbreviated as FJC.

Pipe coatings and field joint coatings are used to protect the pipe fromthe seawater which can cause corrosion. They are also used to providemechanical protection.

Pipes are used to transport fluid having a different temperature thanthe seawater. During the transport of hydrocarbons produced from wellswith high temperatures, the elevated temperature should be maintained.Insulation is therefore needed to prevent heat transfer. Pipe coatingsare also used to provide thermal insulation, and therefore are referredto as thermal insulation coatings.

If a field joint coating is not properly adhered to the pipe coating,and disbondment occurs during the lifetime of the pipe, the temperatureof the hydrocarbon could drop and therefore cause waxes and or hydratesto separate out of the hydrocarbon and form on the internal walls of thepipeline. This could lead to a reduction in the working volume of thepipeline, and possibly eventual blockage of the pipe. Very good adhesionbetween the pipe coating and the field joint coating is thereforeimperative.

Pipe coatings also need to withstand the hydrostatic pressureexperienced at a water depth. Good mechanical properties are thereforealso required.

Several materials are used currently in the industry for the pipecoating, and/or insulation and/or field joint coating. Materials areused for pipe coating and or insulation include polymers. Moreparticularly, polyolefins such as polypropylene (PP) or polyethylene(PE); as well as polyurethane (PU) including glass syntacticpolyurethane (GSPU). Polypropylene is preferred by some overpolyurethane because it does not hydrolize. Hydrolysis can occur inpolyurethane when it is in contact with water. It is accelerated in thepresence of heat. The hydrolysis reactions can also beself-perpetuating, and therefore cause the coating to degradate. This isa known disadvantage of polyurethane.

Moreover, the search for hydrocarbons leads to ever deeper locations atwhich hydrocarbons tend to have higher temperatures. These temperaturestend to accelerate hydrolysis further, making polyurethane less suitablefor future projects including high temperature hydrocarbons.

Although polypropylene is not susceptible to hydrolysis, a knowndisadvantage is that it is more difficult to achieve adhesion betweenpolypropylene and other coating materials. Methods have been developedto increase adhesion to polypropylene pipe coating, but a controlledenvironment is preferable. As stated, field joint coatings are appliedin environments that are less controlled or even exposed to theelements. A method of achieving good adhesion in spite of theenvironment is required.

A common technique used for the production of the joint coating isinjection moulding, such as Injection Moulded Polypropylene (IMPP). Theopposite coating end faces of the two joined pipeline units are usuallyheated, and the pipe joint is enclosed with a mould that defines acavity between the uncoated pipe ends and the pipe joint, the twoopposite coating end faces of the pipeline units and the mould. Moltenpolypropylene is then injected into the cavity, under pressure, where itcools and solidifies. A layer of an anti-corrosion agent such as a typeof epoxy may be provided on the uncoated pipe ends and the pipe joint,as well as an adhesion promoter, before the joint coating (for exampleIMPP) is applied.

A disadvantage of the use of IMPP for the joint coating is that theprocess is time consuming, labour intensive and expensive. Pipelayoperations are usually very time sensitive, due to high day rates of theemployed vessels and labour. With IMPP, a relatively long time isrequired for the polyolefin pipe coating to sufficiently cool and curebefore it can be mobilized and withstand applied stresses. A fast curetime is therefore desirable to reduce the time needed to produce theFJC.

Another disadvantage of using IMPP is that adhesion between thepolypropylene FJC and pipe coating can be difficult to achieve.

WO2010/009559A1 discloses a system having Field Joint Coatings FJC's,see FIG. 10.

SUMMARY OF THE INVENTION

The present invention provides a method of manufacturing a Field JointCoating (FJC), the method comprising:

-   -   providing a pipe section to be joined to a further pipe section        or free end of a pipeline,

wherein each pipe section is provided with a coating comprising:

-   -   a thermal insulation layer which extends over a substantial        portion of the length of the pipe section,    -   an anti-corrosion layer situated underneath the thermal        insulation layer,

wherein the end zones of the pipe section are free of coating,

-   -   connecting the pipe section to the further pipe section or free        end of the pipeline,    -   applying an anti-corrosion coating layer on a connection region        of the joined ends of the pipe section and the further pipe        section or pipeline,    -   heating at least a part of the thermal insulation layer of the        pipe section and the further pipe section or pipeline on either        side of the field joint and applying an intermediate coating        layer of a thermoplastic material over the anti-corrosion        coating layer and over end portions of the thermal insulation        layers on either side of the field joint to provide a continuous        intermediate coating layer in the connection region, wherein the        intermediate coating layer is applied over the anti-corrosion        coating layer and over end faces of the thermal insulation        layers of the joined pipe sections on either side of the field        joint, thereby providing a seal across the connection region,    -   applying a thermal insulation layer on the intermediate coating        layer.

In an embodiment, the thermal insulation layer comprises a protrudingsection which protrudes from a main part of the thermal insulationlayer, wherein the protruding section has a thickness which is smallerthan a thickness of the main part, and wherein the intermediate coatinglayer is applied over at least a portion of an end face of theprotruding section of the thermal insulation layer, and wherein inparticular the protruding section of the thermal insulation layer has alength which is more than twice a thickness of the protruding section ofthe thermal insulation layer.

A primary function of the intermediate coating layer is to seal off thepipe from any ingress of water. Hence, the intermediate coating layermay also be referred to as a “sealing layer”.

In an embodiment, the protruding section of the anti-corrosion layerprotrudes over a distance from underneath the protruding section of thethermal insulation layer.

In an embodiment, the thickness of the protruding section of the thermalinsulation layer is substantially uniform, and the thickness of theprotruding section of the anti-corrosion layer is substantially uniform.

In an embodiment, the anti-corrosion layer has a thickness, and whereinthe protruding section of the anti-corrosion layer protrudes over adistance of at least twice said thickness from underneath the thermalinsulation layer.

In an embodiment, the anti-corrosion layer comprises a protrudingsection which protrudes from underneath the thermal insulation layer andwherein applying the anti-corrosion coating layer of the FJC comprisesapplying a layer of an anti-corrosion coating material onto theconnection region and the protruding section of the anti-corrosionlayer.

In an embodiment, applying the anti-corrosion coating layer comprisesthermally spraying a layer of an anti-corrosion coating material ontothe connection region.

In an embodiment, applying the anti-corrosion layer comprises thermallyspraying a layer of fusion bonded epoxy (FBE) onto the connectionregion.

In an embodiment, pipe sections are provided having an anti-corrosioncoating layer situated under the thermal insulation layer, wherein saidanti-corrosion coating layer comprises protruding sections which extendbeyond the ends of thermal insulation layer, and wherein theanti-corrosion coating layer of the FJC is applied over the protrudingsections of the anti-corrosion coating layer of the pipe sections inorder to form a closed anti-corrosion layer.

In an embodiment, the anti-corrosion coating layer of the pipe sectioncomprises fusion bonded epoxy, and wherein the anti-corrosion layer ofthe FJC comprises fusion bonded epoxy, and wherein during theapplication of the anti-corrosion layer of the FJC, the fusion bondedepoxy of the applied anti-corrosion layer of the FJC bonds with thefusion bonded epoxy of the protruding sections in order to form a closedanti-corrosion layer.

In an embodiment, the thermoplastic material of the intermediate coatinglayer comprises a polyolefine, such as polyethylene or polypropylene.

In an embodiment, applying the intermediate coating layer comprisesthermally spraying a layer of polyolefin such as Polypropylene (PP) ontothe anti-corrosion coating layer.

In an embodiment, the intermediate coating layer is applied in a timeperiod in which the applied anti-corrosion layer has not fully curedyet.

In an embodiment, the polyolefine material comprises 95-100%polypropylene. The remaining 0, 1-5 percent may include additivesincluding copolymers and adhesion promoting molecules.

In an embodiment, the intermediate coating layer is applied over theanti-corrosion coating layer and over protruding end surfaces of thethermal insulation layer of the pipe section and the pipeline to whichthe pipe section has been connected, thereby providing a seal across theconnection region.

In an embodiment of the method, an interface is defined between on theone hand layers of the pipe coating and on the other hand layers of theField Joint Coating, and wherein said interface comprises:

-   -   a first seal in a first region of overlap between the        intermediate coating layer and the thermal insulation layer, and    -   a second seal in a second region of overlap between the        anti-corrosion layer of the FJC and the anti-corrosion layer of        the pipe coating.

In an embodiment of the method, the first and second region of overlapextend substantially parallel to the pipe wall.

In an embodiment of the method, the first region of overlap has a lengthof at least twice a thickness of the protruding section of the thermalinsulation layer, in particular at least three times said thickness, andwherein the second region of overlap has a length of at least twice athickness of the anti-corrosion coating layer, and more in particular atleast five times said thickness.

In an embodiment the protruding end surfaces of the thermal insulationlayer may be between 1 and 50 mm in length.

In an embodiment the protruding section of the thermal insulation layermay be less than 6 mm in height.

In an embodiment, the intermediate coating layer is treated with asurface treatment and/or a primer prior to the application of thethermal insulation layer.

In an embodiment, the thermal insulation layer of the FJC comprises:

-   -   polyDiCycloPentaDiene (pDCPD), and/or    -   silicone material and/or    -   a modified polyether or    -   a polypropylene material    -   a polyurethane material

In an embodiment, the thermal insulation layer of the FJC comprisessilicone material with a polypropylene additive.

In an embodiment, the silicone material comprises 2-30 percentpolypropylene by weight, based on the combination of silicone andpolypropylene. The polypropylene material may be modified polypropylene.The polyurethane material may be modified polyurethane.

The PP or PU may be modified in that there may be additives included inthe material to help with adhesion and/or additives to reduce hydrolysisin the case of PU.

In an embodiment, applying the thermal insulation layer of the FJCcomprises injection moulding.

The present invention further relates to a pipeline comprising a seriesof interconnected pipe sections, each pipe section comprising a coatingcomprising:

-   -   a thermal insulation layer which extends over a substantial        portion of the length of the pipe section,    -   an anti-corrosion layer situated underneath the thermal        insulation layer,

wherein the pipeline comprises Field Joint Coatings (FJC) at connectionregions where the ends of the adjacent pipe sections are interconnected,wherein each Field Joint Coating comprises:

-   -   an anti-corrosion coating layer,    -   an intermediate coating layer of a thermoplastic material which        covers the anti-corrosion coating layer, wherein the        intermediate coating layer extends over end faces of the thermal        insulation layer of the pipe sections on either side of the        Field Joint Coating, thereby forming a seal across the        connection region,    -   a thermal insulation layer which covers the intermediate coating        layer.

In an embodiment, the pipe sections between the FJC's comprise ananti-corrosion coating layer which comprises protruding sections whichextend beyond the thermal insulation layer towards the ends of the pipesections, and wherein the anti-corrosion layer of each FJC extends overthe protruding sections of the anti-corrosion coating layer of the pipesections in order to form a continuous anti-corrosion layer.

In an embodiment, the anti-corrosion layer of the pipe sectionscomprises a layer of epoxy, and wherein the anti-corrosion layer of theFJC's comprises a layer of epoxy, wherein the layer of fusion bondedepoxy of the pipe sections comprises protruding sections which extendbeyond the thermal insulation layer of the pipe sections, the protrudingsections being covered by and connected to the fusion bonded epoxy ofthe anti-corrosion layer of the FJC.

In an embodiment, the intermediate coating layer comprises polyolefine,such as polyethylene or polypropylene (PP).

In an embodiment, the intermediate coating layer has a thickness of 0.01mm-10 mm.

In an embodiment, the intermediate coating layer extends over endsurfaces of a thermal insulation of the pipe sections on either side ofthe Field Joint Coating, thereby forming a seal across the connectionregion.

In an embodiment, the intermediate coating layer extends at least overend surfaces of a protruding section of the thermal insulation layer ofthe pipe sections on either side of the Field Joint Coating.

In an embodiment, the thermal insulation layer of the Field JointCoating comprises:

-   -   polyDiCycloPentaDiene (pDCPD), and/or    -   silicone, and/or    -   a modified polyether.

The present invention further relates to a pipe section, constructed tobe connected with a further pipe section or free end of a pipeline in anend-to-end relationship, the pipe section comprising a coatingcomprising:

-   -   a thermal insulation layer which extends over a substantial        portion of the length of the pipe section,    -   an anti-corrosion layer situated underneath the thermal        insulation layer,        wherein opposing end zones of the pipe section are free of any        anti-corrosion layer or thermal insulation layer in order to        allow a welding operation at the ends of the pipe section,        wherein the anti-corrosion coating layer and the thermal        insulation layer stop at a distance from the ends of the pipe        section, wherein the anti-corrosion coating layer comprises        protruding sections which extend beyond the thermal insulation        layer.

In an embodiment, the anti-corrosion coating layer comprises fusionbonded epoxy.

In an embodiment the anti-corrosion layer comprises a liquid epoxy.

In an embodiment, the thermal insulation layers are comprised ofpolypropylene. The present invention further relates to an assembly forproviding a field joint coating (FJC) to a pipeline, the assemblycomprising:

-   -   a first heating device for heating at least a part of the        thermal insulation layer, in particular the protruding sections,    -   a first coating device for providing an anti-corrosion coating        layer,    -   a second coating device for providing an intermediate coating        layer of a thermoplastic material,    -   a thermal insulation depositing device for providing a thermal        insulation layer.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments of the invention will be described by way of example only,with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts.

FIGS. 1A, 1B, 1C and 1D show the production and installation of pipelineoffshore using the S-lay and J-lay methods.

FIG. 1E shows the installation of a pipeline offshore using the reel-laymethod

FIG. 1F shows an example of a spool base where FJC's are applied priorto spooling the pipeline on a reel.

FIG. 2 shows a partial sectional view of a Field Joint Coating accordingto the invention.

FIG. 3A shows another sectional view of a Field Joint Coating accordingto the invention.

FIG. 3B shows a sectional view of a detail of FIG. 3A.

FIG. 3C shows another sectional view of a Field Joint Coating accordingto the invention, with a water ingress path being indicated.

FIG. 4 shows a sectional view of a Field Joint Coating across to twojoined pipe sections.

FIG. 5 shows a partial sectional view of an alternative embodiment.

DETAILED DESCRIPTION OF THE FIGURES

Turning to FIGS. 1A, 1B, 1C, 1D, offshore pipelines may be constructedin several ways. FIGS. 1A and 1B show an S-Lay vessel 1 constructing apipeline 2 using the S-Lay method. In the S-lay method, the pipeline 2is launched over a stinger 3 and laid in the form of an “S” between thesea surface 4 and the seabed 5. Line pipe is fabricated in typical jointlengths of 12.2 m (40 ft), sometimes 18.3 m (60 ft) length. In the S-Laymethod, single pipe joints 6 are added to the most forward end of thepipeline 2, several work stations 7 performing a part of the pipelineconstruction process, a few stations completing the weld, one stationinspecting the weld and one or two stations completing the field jointcoating. As an alternative, in the S-Lay method, multiple joints, forinstance double joints may be added to the end of the pipeline 2 insteadof the single joint 6, the double joints being constructed from twosingle joints, either in a separate construction area on board the S-Layvessel 1 or in a factory onshore.

The word pipeline may also indicate a Steel Catenary Riser (SCR).

FIGS. 1C and 1D show a J-Lay vessel 11 constructing the pipeline 2 usingthe J-lay method. The pipeline 2 is laid in the form of a ‘J’ betweenthe sea surface 4 and the seabed 5. In the J-Lay method, multi-jointpipe sections 13 are added to the most upward end of the pipeline 2, thepipeline construction process being typically completed in one or twowork stations 15. The multi-joints 13 are constructed from a number ofsingle joints 14, either in a separate construction area on board theJ-Lay vessel 11 or in a factory onshore or in a combination of both.

All pipeline construction processes have a high number of similar weldsto be made either in a more or less horizontal pipe position and/or in amore or less vertical pipe position. The welds are generally referred toas field joints. The making of a field joint may be performed on thecritical path of the pipeline laying operation, so time is an importantfactor.

FIG. 1E shows another method of pipeline laying which is generallyreferred to as reeling. In reeling, a relatively long length of pipe isspooled from a reel and laid on the seafloor. When the entire length islaid, a new, full reel with a new length is put in place and the pipesection on the new, full reel is connected with a weld to the trailingend of the laid pipe section.

FIG. 1F shows in top view the spooling of a pipeline 2 at a spool base17 from land onto a reel 16 positioned on a transport barge 19 which cantransport the reel to a reeling vessel. Generally, several pre-assembledlengths of pipeline, called stalks, are spooled onto a single reel. Thestalks are interconnected by a field joint which is made in a workstation 18 just prior to spooling the stalk onto the reel.

After the weld is made, the bare metal of the pipe at the field jointgenerally needs to be covered with mechanical insulation, thermalinsulation and/or an anti-corrosion coating. Any combination of theseprotection layers which are applied after welding the field joint isgenerally called Field Joint Coating, i.e. the coating of the fieldjoint. This is a separate step in the pipeline laying operation which isperformed on the critical path both on the pipelay vessel 1 and on thespool base 17, as shown in FIG. 1F. A same layer may provide bothmechanical protection and thermal insulation.

Turning to FIG. 2, a field joint 20 according to the prior art is shown.A first pipe 22 is connected to a second pipe 24. The pipes 22, 24 arepositioned in an end-to end-relationship, wherein an end 26 of the firstpipe 22 abuts an end 28 of the second pipe 24. It will be clear that thepipes 22, 24 are only partially shown. The pipe 24 may form the free endof a pipeline 2 which is suspended from a pipeline laying vessel 1. Theweld 30 connects the two ends of the pipes 22, 24.

Each pipe is covered with a coating 25 which comprises an anti-corrosionlayer 32, which may be of fusion bonded epoxy. Other coating layers arealso known. The coating 25 of each pipe further comprises a thermalinsulation layer 34, which may be manufactured from a polyolefine suchas polypropylene or polyethylene. The thermal insulation layer mayprovide thermal insulation and mechanical protection at the same time.Generally, the thermal insulation layer 34 is thicker than theanti-corrosion layer 32.

The anti-corrosion layer 32 and thermal insulation layer 34 are appliedon the pipe sections 22, 24 in a controlled environment, generally onshore and prior to the transportation of the pipes to the pipelinelaying vessel. This allows a fast and well controlled operation leadingto a high quality.

The anti-corrosion coating layer 32 and the thermal insulation layer 34extend over the greater portion of the pipe, i.e. 80 to 90 percent ofthe length of the pipe. The anti-corrosion coating layer 32 and thethermal insulation layer 34 stop at a distance 36 from the pipe ends 26,28, so that end zones 38 are provided as bare metal. This allows forwelding, inspection of the weld, and the possibility of one or more cutouts in case the weld does not meet the requirements and cannot berepaired.

In the field, the only section that needs to be coated is the area 40around the field joint 20. This is generally called a Field JointCoating 42.

Turning to FIGS. 3A and 3B, an operation of Field Joint Coating a fieldjoint 40 according to the invention is shown. The pipe 22 is shown withthe coating 25 comprising an anti-corrosion coating layer 32 and athermal insulation layer 34. The thermal insulation layer 34 comprisesan inclined end face 49 of a main part 35 of the thermal insulationlayer 34, and a protruding section 33. The protruding section 33 extendsover a length 65 from the end face 49 of the main part 35 of the thermalinsulation layer. The length 65 of the protruding section 33 may be atleast twice a thickness 61 of the protruding section 33 of the thermalinsulation layer 34, in particular at least three times the thickness ofthe protruding section.

The anti-corrosion layer 32 may be fusion bonded epoxy, and the thermalinsulation layer 34 may be polypropylene. The protruding section 33 endsin an inclined end face 50, which extends at an angle α of about 20-50degrees to a pipe axis. The inclined end face 49 of the main part 35 isoriented in a similar angle of about 20-50 degrees to a pipe axis. Theend face 49 forms the end face of a main part of the thermal insulationlayer 34 and the end face 50 forms the end face of the protrudingsection 33 of the thermal insulation layer 34.

The end face 50 of the protruding section 33 is non-aligned with the endface 49 of the main part 35. The protruding section 33 has an outersurface 47 which may extend parallel to the pipe wall. The outer surface47 of the protruding section is non-aligned with the end face 49 of themain part. The thickness 61 of the protruding section 33 may be lessthan one third of a thickness 63 of the main part 35 of the thermalinsulation layer 34. The thickness 61 of the protruding section 33 ofthe thermal insulation layer 34 is substantially uniform over its length65.

The anti-corrosion coating layer 32 of the pipe sections extends beyondthe protruding thermal insulation 33 over a length 52 and forms aprotruding section 53 of the anti-corrosion coating layer 32. Thedistance 52 is at least twice as large as a thickness 102 of theanti-corrosion coating layer 32, and more in particular at least fivetimes a thickness 102 of the anti-corrosion coating layer 32. Theprotruding section 53 of the anti-corrosion coating layer 32 has an endface 104. The end face 104 is non-aligned with the end face 50 of theprotruding section 33 of the thermal insulation. The protruding section53 has an outer surface 108 which extends parallel to the pipe wall.

The thickness 102 of the protruding section 53 of the anti-corrosioncoating layer 32 is substantially uniform over its length 52.

The outer surface 108 of the protruding section 53 of the anti-corrosioncoating layer 32 extends parallel to the outer surface 47 of theprotruding section 33 of the thermal insulation layer 34.

The end zone 38 of the pipe section 22 is bare metal, as is the end zone38 of the pipe section 24.

In the method of applying a Field Joint Coating according to theinvention, an anti-corrosion layer 60 is applied on the bare metal ofthe area 40 around the field joint 20. The anti-corrosion layer 60 maybe an epoxy such as a fusion bonded epoxy. The anti-corrosion layer 60overlaps the protruding section 53 of the anti-corrosion layer 32 of thepipe section 22 in a region of overlap 106. Said region of overlap 106extends parallel to the pipe wall. The region of overlap 106 extendsover a length 52 which may be similar to the length 52 of the protrudingsection 53 of the anti-corrosion layer 32. In other words, theanti-corrosion layer 60 of the FJC overlaps the entire protrudingsection 53 of the anti-corrosion layer 32 of the pipe section 22. Theanti-corrosion layer 60 bonds with the anti-corrosion layer 32 of thepipe section 22 at the protruding section 53 and forms a second seal132. In the region of overlap 106, the anti-corrosion layer 60 of theFJC extends parallel to the pipe wall.

The anti-corrosion coating layer 60 may be applied by thermal spraying,i.e. by heating the material of the anti-corrosion layer and sprayingfine droplets of said material onto the area 40. There are other methodsof applying the anti-corrosion layer.

The anti-corrosion coating layer 60 may have a thickness of between 0.01mm and 1 mm.

The anti-corrosion layer 32 of the pipe section and the anti-corrosionlayer 60 of the field joint together form a closed anti-corrosion layerover the field joint.

An adhesion promoter may be applied over the anti-corrosion layer.

In a next step, an intermediate coating layer 62 of a polymer is appliedonto the anti-corrosion layer 60, or adhesion promoter. Preferably, theintermediate coating layer 62 is thermally sprayed. The intermediatecoating layer 62 is sprayed over at least a part of the end faces 50 ofthe thermal insulation 34 of the pipe section.

Preferably, the intermediate coating layer 62 is polypropylene, and thethermal insulation 34 of the pipe sections is also polypropylene.

The intermediate coating layer 62 bonds with the thermal insulationlayer 34, i.e. the protruding section 33 thereof in the region ofoverlap 54 at the end face 50. In this way, a first seal 130 is formedin the region of overlap. The two seals 130 132 are named “first” seal130 and “second” seal 132, because any water ingress coming from theoutside will first meet the first seal 130 and subsequently meet thesecond seal 132. In the method of making the FJC, the first seal 130 ismade after the second seal 132.

The intermediate coating layer 62 may also be applied over a part of orthe whole of an outer side 47 (or outer surface) of the protrudingsection 33 and over a part or the whole of the end face 49 and may alsobond to the thermal insulation layer in this region. Therefore, theregion of overlap 54 may extend from a foot 69 of the end face 50 to atop 71 of end face 49.

The intermediate coating layer 62 may have a thickness of between 0.01mm and 10 mm.

The intermediate coating layer is sprayed by thermal spraying,preferably before the anti-corrosion layer has fully cured.

Two continuous layers are hence provided, a first layer comprising theanti-corrosion coating layer 32 of the pipe section and theanti-corrosion layer 60 of the field joint, and a second closed layercomprising the intermediate coating layer 62 of the field joint and thethermal insulation 34 of the pipe section.

Turning to FIG. 4, the intermediate coating layer 62 may subsequently betreated for bonding with the thermal insulation layer 70 of the FieldJoint Coating 42. The treating step may comprise applying a primer andor surface treatment, for instance roughening the surface of theintermediate coating layer 62.

In a next step, the thermal insulation layer 70 of the field jointcoating 42 is applied.

Due to the size of FIG. 4, the anti-corrosion layers 32, 60 are notseparately shown, but the skilled person will understand that theselayers are present nonetheless.

The thermal insulation layer 70 may be composed of polyDiCycloPentaDiene(pDCPD), and/or silicone, and/or a modified polyether. Preferably thethermal insulation layer 70 is fast-curing.

The thermal insulation material polyDiCycloPentaDiene has a short geltime of about 20-25 seconds for FJC. This means that the field joint canbe launched into the sea very soon after the coating has been applied.This allows a faster pipeline laying process.

During research, the thermal insulation material polyDiCycloPentaDienewas further found to show a very good adhesion to PP, with adhesiontensions being in the order of 12 Mpa.

The thermal insulation layer 70 may be applied by injection moulding, aprocess which is known in the field of the art. The thermal insulationlayer 70 covers the intermediate coating layer and fills the spacebetween the end faces 49, 50 on either side of the field joint 20. Thethermal insulation layer 70 may cover the end sections 72 of the thermalinsulation layers 34 of the pipe sections 22, 24 over a certain distance74.

The Field Joint Coating 42 is now finished, and the field joint may belowered into the water from the pipeline laying vessel.

The Field Joint Coating 42 has an advantage of both good thermalinsulation and low water ingress. Turning to FIG. 3C, the group oflayers 32, 34 forming the coating 25 of the pipe section on the one handand the group of layers 60, 62, 70 forming the FJC on the other handdefine an interface 120. The interface 120 is indicated with a thickdashed line, The interface 120 defines the path along which water shouldtravel in order to reach the pipe 22 and corrode the pipe. It will beunderstood that the interface 120 is actually a surface which extendsabout the pipe 22, and that on the opposite side of the weld a sameinterface 120 is present at the transition of the FJC and the coating 25of pipe 24.

The interface 120 has a total length 126 from the outside 122 to theposition where the interface 120 reaches the pipe 22. The length 126 ofthe interface 120 is greater than twice the thickness 63 of the thermalinsulation layer 34. The length 126 of the interface 120 issubstantially greater than a corresponding length of an interface of thesystem of WO2010/009559, see FIG. 10. When travelling from the outside122 to the point 124 where the transition reaches the pipe, theinterface 120 comprises two regions of overlap:

-   -   a first region of overlap 54 defining a first seal 130 between        the intermediate coating layer 60 of the FJC and the thermal        insulation layer 34 of the pipe 22 section, and    -   a second region of overlap 106 defining a second seal 132        between the anti-corrosion layer 60 of the FJC and the        protruding section 53 of the anticorrosion layer 32 of the pipe        22.

Both regions of overlap 54, 106 i.e. both seals 130, 132 are relativelylong and have a good bonding between respectively the intermediatecoating layer 60 of the FJC and the thermal insulation layer 34 of thepipe 22 section, and between the anti-corrosion layer 60 of the FJC andthe protruding section 53 of the anti-corrosion layer 32 of the pipe 22.Therefore, water ingress is prevented by the two subsequent seals 130and 132. As a result, water ingress is more difficult than in the systemof WO2010/009559. The present invention therefore provides a substantialimprovement over WO2010/009559 in terms of prevention of water ingress.

Turning to FIG. 5, an alternative embodiment is provided wherein theprotruding section 33 of the thermal insulation layer (34) is notpresent, and wherein the intermediate coating layer 62 covers the endface 49 directly. This embodiment also has a first seal 130 and a secondsingle seal 132. The first seal 130 is formed by the intermediatecoating layer 62 overlapping the end face 49 in the region of overlap54, and the second seal 132 is formed by the anti-corrosion layer 60 ofthe FJC overlapping the anti-corrosion layer 32 of the pipe in theregion of overlap 106. This embodiment is also a substantial improvementover WO2010/009559, because due to their length, the first seal 130 andsecond seal 132 have a higher water blocking capability than can berealized with the system of WO2010/009559.

It will be apparent to those skilled in the art that variousmodifications can be made to the pipeline unit, assembly and methodwithout departing from the scope of the invention.

The invention claimed is:
 1. A method of manufacturing a Field JointCoating (FJC), the method comprising: providing a pipe section to bejoined to a further pipe section, wherein each pipe section is providedwith a coating comprising: a thermal insulation layer which extends overa substantial portion of the length of the pipe section, and ananti-corrosion layer situated underneath the thermal insulation layer,wherein end zones of the pipe section are free of coating, connectingthe pipe section to the further pipe section to form a field joint,applying an anti-corrosion coating layer on a connection region of thejoined ends of the pipe section and the further pipe section, heating atleast a part of the thermal insulation layer of the pipe section and thefurther pipe section on either side of the field joint and applying anintermediate coating layer of a thermoplastic material over theanti-corrosion coating layer and over end faces of the thermalinsulation layers on either side of the field joint to provide acontinuous intermediate coating layer, wherein the continuousintermediate coating layer is applied over the anti-corrosion coatinglayer and over end faces of the thermal insulation layers of the joinedpipe sections on either side of the field joint, and wherein thecontinuous intermediate coating layer is allowed to bond with thethermal insulation layers of the joined pipe sections on either side ofthe field joint, thereby providing a seal across the connection region,and applying a FJC thermal insulation layer on the continuousintermediate coating layer, wherein the thermal insulation layercomprises a protruding section which protrudes from a main part of thethermal insulation layer, wherein the protruding section of the thermalinsulation layer has a thickness which is smaller than a thickness ofthe main part of the thermal insulation layer, wherein the protrudingsections of the thermal insulation of the pipe sections comprise anouter side which extends substantially parallel to a pipe axis, andwherein the continuous intermediate coating layer is applied over atleast a portion of the outer side of the protruding sections on eitherside of the field joint.
 2. The method of claim 1, wherein theanti-corrosion layer of each pipe section comprises a protruding sectionwhich protrudes from underneath the thermal insulation layer over alength, and wherein applying the anti-corrosion coating layer of the FJCcomprises applying a layer of an anti-corrosion coating material ontothe connection region and the protruding section of the anti-corrosionlayer.
 3. The method of claim 2, wherein the anti-corrosion layer has athickness, and wherein the protruding section of the anti-corrosionlayer protrudes over a distance of at least twice said thickness fromunderneath the thermal insulation layer.
 4. The method of claim 2,wherein the protruding section of the thermal insulation layer has alength which is more than twice a thickness of the protruding section ofthe thermal insulation layer.
 5. The method of claim 4, wherein theprotruding section of the anti-corrosion layer protrudes over a distancefrom underneath the protruding section of the thermal insulation layer,wherein the thickness of the protruding section of the thermalinsulation layer is substantially uniform, wherein the thickness of theprotruding section of the anti-corrosion layer is substantially uniform,and wherein the intermediate coating layer is applied over at least aportion of an end face of the protruding section of the thermalinsulation layer.
 6. The method of claim 4, wherein applying theintermediate coating layer comprises thermally spraying a layer ofthermoplastic material onto the anti-corrosion layer and at least a partof the protruding section of the existing layer of thermal insulation,wherein the protruding section of the thermal insulation layer is heatedprior to applying the intermediate coating layer, and wherein theintermediate coating layer is fused to the protruding sections of thethermal insulation layers of the pipe sections on either side of thefield joint to form one continuous layer across the field joint.
 7. Themethod of claim 1, wherein the further pipe section forms the free endof a pipeline.